1. Field of the Invention
The present invention relates to systems and methods for protecting vehicle occupants from injury. More specifically, the present invention relates to a dual stage inflator for a vehicular airbag system that provides extended gas delivery by injecting multiple gas flows into an airbag system such as an inflatable curtain.
2. Description of Related Art
The inclusion of inflatable safety restraint devices, or airbags, is now a legal requirement for many new vehicles. In addition to this, inflatable airbags enjoy widespread acceptance for use in motor vehicles and are credited with preventing numerous deaths and injuries. Some studies estimate that the use of frontally placed airbags reduces the number of fatalities in head-on collisions by 25% among drivers using seat belts and by more than 30% among unbelted drivers. Other research suggests that in a frontal collision, the combination of a seat belt and an airbag can reduce serious chest injuries by 65% and serious head injuries by up to 75%. These numbers and the thousands of prevented injuries they represent demonstrate the life-saving potential of airbags and the need to encourage their use, production, and development.
As a result in part of benefits such as those described above, automakers are now required to install airbags in most new vehicles bound for sale in the United States. Many automobile manufacturers have turned this requirement of implementation of airbag technology into a marketing tool. Enticed by the promise of added safety, vehicle purchasers frequently seek out vehicles with sophisticated airbag systems.
Airbags are typically installed in the steering wheel and in the dashboard on the passenger side of a car. In the event of an accident, an accelerometer situated within the vehicle measures the abnormal deceleration caused by the accident and triggers the expulsion of rapidly expanding gases from an inflator into each of the airbags. The expanding gases rapidly fill the airbags, which immediately inflate in front of the driver and passenger to protect them from impact against the windshield, dashboard, or steering wheel. Thus used, vehicular airbags have saved countless human lives.
As a result of the success of front-installed airbags, other airbags designed to protect occupants in other types of vehicular collisions have been developed. Side impact airbags, often in the form of inflatable curtains, were one such airbag developed in response to the need for protection from impacts in a lateral direction, or against the side of the vehicle. Such curtains are placed along the side of a vehicle in places such as the ceiling or roof rails. An inflatable curtain may be composed of one or more separately inflated cushions that protect individual passengers in different positions within the vehicle.
Side impact cushions are often designed to unfold or unroll downward from their installation site to inflate beside a vehicle occupant to keep the vehicle occupant from hitting the door or window during a lateral impact event. Since the vehicle occupant may be leaning forward, reclined in the seat, or at any position between, such cushions are often made somewhat long to ensure that even such an “out-of-position” occupant hits the cushion.
In some installations, multiple cushions may be fed by a single inflator as a result of space constraints or other considerations. The inflator may be placed at either end of a cushion. In situations where multiple cushions are fed by a single inflator positioned either fore or aft of the cushions, an especially long gas flow path exists between the inflator and the cushion furthest from the inflator. This long gas flow path may reduce the speed of the gas flow, thus resulting in delayed inflation of the furthest cushions. Furthermore, the outermost extents of an inflatable curtain in such an installation may receive insufficient inflation gas pressure to inflate the curtain to the optimal protective pressure.
Even in somewhat shorter cushions, rapid and even inflation can be difficult to achieve with known inflator designs. Many existing inflators eject inflation gases outward radially. As a result of this, the inflation gases are not propelled along the length of the cushion with sufficient force to reach its outer edges, but are instead largely directed into the cushion near the inflator. The outer regions of the cushion are thus inflated later than those closest to the inflator.
Additionally, some inflatable curtain systems are somewhat expensive due to the need for multiple inflators, attachment mechanisms, and the like. Many inflatable curtain systems require the use of a “gas guide,” or conduit that conveys gas from the inflator to the inflatable curtain.
In addition to this, in collisions which result in vehicle rollovers, the time period during which a vehicle occupant may be injured by striking a lateral side of the vehicle is often much longer than in a conventional collision. As a result of this, it would be beneficial to the occupants for the airbags to remain inflated during that period in order to protect them from injury. Conventional inflators, however, are largely incapable of providing such a long period of inflation.
Further, in some collisions, it would be beneficial for an airbag inflator to be “smart,” or capable of providing different amounts of gas to an airbag to inflate it to different levels of hardness in response to different collisions. Most currently known airbags are capable of providing a single inflation pressure. Similarly, it would be beneficial to provide an inflator that is capable of producing a second flow of inflation gas at a controllable delay from a first flow of inflation gas in order to either maintain inflation of an airbag or reinflate an airbag.
Accordingly, a need exists for an inflator and related methods that remedy problems found in the prior art. Such an inflator should preferably provide relatively even and rapid inflation of an associated inflatable curtain, preferably without requiring multiple inflators for a single curtain. Such an inflator should also preferably be simple and inexpensive to manufacture and install.